It is now well established that cellular interactions are at least in part mediated by receptor/ligand interactions. One class of receptors is known to recognize the peptide sequence "RGD"; other receptors recognize carbohydrate ligands.
One class of receptors that recognize carbohydrate-based ligands mediates the adhesion of circulating neutrophils to stimulated vascular endothelium. This is a primary event of the inflammatory response and appears to be involved as well in allergic and autoimmune responses. Several receptors have been implicated in this interaction, including a family of putative lectins that includes gp90.sup.MEL (Leu8), ELAM-1, and GMP-140 (PADGEM) and (Gong, J. G., et al., Nature (1990) 343:757; Johnston, G. I., et al., Cell (1989) 56:1033; Geoffrey, J. S., and Rosen, S. D., J. Cell Biol. (1989) 109:2463; Lasky, L. A., et al., Cell (1989) 56:1045). These lectins have been termed L-SELECTIN, E-SELECTIN, and P-SELECTIN.
E-SELECTIN is perhaps the best characterized of the three selectins. It is particularly interesting because of its transient expression on endothelial cells in response to IL-1 or TNF (Bevilacqua, M. P., et al., Science (1989) 243:1160). The time course of this induced expression (2-8 hours) suggests a role for this receptor in initial neutrophil extravasation in response to infection and injury. Furthermore, Bevilacqua et al. (see Bevilacqua, M. P., et al., Proc. Natl. Acad. Sci. USA (1987) 84:9238) have demonstrated that human neutrophils or HL-60 cells will adhere to COS cells transfected with a plasmid containing a CDNA encoding for the E-SELECTIN receptor. Information regarding the DNA sequences encoding for endothelial cell-leukocyte adhesion molecules are disclosed within PCT published application WO90/13300 published Nov. 15, 1990.
Recently, several different groups have published papers regarding the ligand for E-SELECTIN. Lowe et al., (1990) Cell, 63:475-484 reported a positive correlation between the E-SELECTIN dependent adhesion of HL-60 cell variants and transfected cell lines, with their expression of the sialyl Lewis x (sLex) oligosaccharide, Neu NAC .alpha.2-3-Gal-.beta.1-4(Fuc .alpha.1-3)-GlCNAc. By transfecting cells with plasmids containing an .alpha.(1,3/1,4) fucosyltransferase, they were able to convert non-myeloid COS or CHO lines into sLex-positive cells that bind in an E-SELECTIN dependent manner. Attempts to block E-SELECTIN dependent adhesion using anti-sLex antibodies were uninterpretable due to the agglutination of the test cells by the antibody. They concluded that one or more members of a family of oligosaccharides consisting of sialylated, fucosylated, lactosaminoglycans are the ligands for the lectin domain of E-SELECTIN. Phillips et al., (1990) Science, 250:1130-1132 used antibodies with reported specificity for sLex to inhibit the E-SELECTIN dependent adhesion of HL-60 or LEC11 CHO cells to activated endothelial cells. Liposomes containing difucosylated glycolipids with terminal sLex structures inhibited adhesion, while those containing nonsialylated Lex structures were partially inhibitory. Walz et al., (1990) Science, 250:1132-1135 were able to inhibit the binding of a E-SELECTIN-IgG chimera to HL-60 cells with a monoclonal antibody directed against sLex or by glycoproteins with the sLex structure, but could not demonstrate inhibition with CD65 or CD15 antibodies. Both groups concluded that the sLex structure is the ligand for E-SELECTIN. U.S. Pat. No. 5,211,937, issued May 18, 1993, assigned to the present assignee and incorporated herein by reference discloses and claims the foregoing minimum tetrasaccharide structure and identifies the groups putatively interactive with the ELAM-1 receptor.
In contrast to E-SELECTIN, the properties of the ligands that bind to L-SELECTIN and P-SELECTIN are not as well worked out. L-SELECTIN appears to bind a sialic acid bearing ligand based on neuraminidase treatment of peripheral lymph node high endothelial venules which inhibits L-SELECTIN recognition. True et al., 1990, J. Cell Biol. 111,2757-2764. Further, other studies using soluble L-SELECTIN in direct binding/inhibition assays suggests that certain carbohydrate moleties may be important ligand components including mannose and fucose, particularly when sulfated or phosphorylated. Imai et al., 1990 J. Cell Biol. 111, 1225-1232. More recent studies suggest that L-Selectin binds to sialyl Lewis X. Foxall, C., et al., Cell (1992) 117:895-902.
The ligand to P-SELECTIN is thought to have an epitope related to sialyl Lewis x. This conclusion is based on studies using antibody with this specificity that block P-SELECTIN mediated adhesion of HL-60 cells to activated platelets or COS cells that express P-SELECTIN. Larsen et al. (1990) Cell 63, 467-474. Other experiments have shown that the adhesion of HL-60 cells to P-SELECTIN transfected cells is blocked by the pentasaccharide isolated from milk that has the Lewis.sup.x epitope. Recently, P-Selectin has been shown to bind to sulfatides. Aruffo, A., et al. (1991) Cell, 67:35-44.
Because of the role of selectins in disease, particularly diseases involving unwanted cell-cell adhesion that occurs through selectin-ligand binding on defined cell types, the identification and isolation of novel ligands that would permit the regulation of such selectin-ligand binding is sorely needed.
One of the modes of action of compounds of the invention involves modulating cell-cell adhesion events and is thought to be via selectin-ligand binding. However, it is noteworthy that the additional biological mechanism(s) of action which accounts for the myriad medical activities of compounds of the invention, and derivatives and salts thereof, is not known.